In the first part of the talk, the idea of tunnel injection(TI) of carriers from a semiconductor quantum well (QW) to self-assembled quantum dots (QDs) through a thin separation barrier will be presented. The idea was proposed almost two decades ago to increase the modulation speed and carrier collection efficiency of quantum dot-based semiconductor lasers [1,2]. Particularly, the presentation will be focused on the results from low-temperature optical spectroscopy and carrier relaxation dynamics in the GaAs- and InP-based QW-QDs tunnel injection structures [3-7]. The latter TI system is proposed as an active part of QD-based lasers operating in the C-band (1550 nm) of silica fibres and dedicated to long-haul fiber-based telecom networks. The problem of electronic coupling between QW and QDs confined states will be highlighted that defines the overall electron-hole recombination dynamics on the ground state of the coupled QW-QDs system and general carrier relaxation pathways [5,6]. Also, the existence of carrier relaxation bottleneck will be discussed that hampers the fast feeding process of the lasing state and must be carefully addressed in the future realisations utilising the TI scheme.
The second part of the talk will be focused on a single photon source (SPS) based on a self-assembled InAs/InP semiconductor QD emitting close to 1550 nm. Such SPS are dedicated to quantum-secured, long-haul telecom fibre networks. Results from single dot spectroscopic experiments will be presented, including high-spatial and spectral resolution photoluminescence and interferometric experiments revealing a specific correlation between single photon emission acts [8-10]. This part of the talk will be concluded by showing necessary future steps toward the practical realisation of the SPS based on InAs/InP QDs.